1. Field of the Invention
The invention pertains to an actuation system for a friction clutch installed in the drive train of a motor vehicle, especially a commercial motor vehicle, between a drive unit, especially an internal combustion engine, and a transmission. This actuation system includes a pressure medium-powered cylinder assembly which is used to actuate the friction clutch; a pilot/automatic control valve assembly connected to the source of the pressure medium, by means of which the pressure medium-powered cylinder assembly can be actuated as a function of a control input representing a desired actuation state, possibly the desired position of a disengaging device, and an actual value representing an actual actuation state, possibly the actual position of the disengaging device. An auxiliary actuating assembly is provided for clutch actuation independently of the ability of the valve assembly to function and/or independently of the ability of a pilot/automatic control unit driving the valve assembly to function and/or independently of the instantaneous pressure of the pressure being made available by the pressure medium source.
2. Description of the Related Art
An actuation system of this type is known from, for example, DE 197 16 600 A1, the disclosure of which is incorporated herein by reference.
In the known actuation system, the actual position of a disengaging bearing assembly is detected by a hydraulic measuring cylinder assembly, which cooperates with a pilot/automatic control valve assembly operating according to the principle of the pressure scale. The pressure medium-powered cylinder assembly, which can be designed, for example, as a pneumatic cylinder, is actuated via the pilot/automatic control valve assembly as a function of the actual value detected by hydraulic means and a hydraulic signal, which represents the control input and which is transmitted by a hydraulic master cylinder associated with a clutch pedal assembly. According to a variant, the hydraulic measuring cylinder assembly is designed as a slave cylinder assembly, which acts on the disengaging bearing assembly. The slave cylinder assembly is used for the emergency or auxiliary actuation of the clutch. According to another variant, a hydraulic slave cylinder assembly is provided in addition to the pneumatically powered cylinder assembly to make possible an emergency or auxiliary actuation of the clutch.
An emergency or auxiliary actuation of the friction clutch is desirable for a number of different reasons. For example, after the vehicle in question has been parked for a certain period of time, the compressed air tank of the pressure medium source can become completely empty as a result of leaks in the individual receivers. If the vehicle was parked with a gear engaged, the tension of the drive train would make it impossible to disengage the gear without emergency or auxiliary actuation of the clutch, and the vehicle""s engine could therefore not be started to fill the compressed air tank back up again. Auxiliary actuation of the clutch is therefore extremely important in practical terms, both for passenger and commercial vehicles.
An extremely high degree of operational reliability is also required for commercial vehicles for another reason. It is generally known, for example, that various components, such as electronic components, can fail and that in such a situation the vehicle must be taken to the nearest garage still under its own power if possible and possibly in a manner deprived of a certain convenience. We speak in this situation of a so-called xe2x80x9climp-homexe2x80x9d function.
In themselves, these requirements are fulfilled by the known solutions according to DE 197 16 600 A1. An auxiliary actuation system designed in this way, however, suffers from several disadvantages. For example, the auxiliary actuation of a clutch of this type requires the driver to exert a great deal of force on the clutch pedal, which the driver can do only with great effort. In addition, the auxiliary actuation system represents a high degree of mechanical and hydraulic complexity. For example, a master cylinder assembly designed for high pressures, an appropriately massive clutch pedal, and a hydraulic slave cylinder assembly designed for high pressures (and possibly a measuring cylinder assembly) are all required. Because the components must be very strong, they must also be correspondingly heavy and bulky. The auxiliary actuation system therefore also occupies a considerable amount of space. In addition, it is disadvantageous on principle to provide a hydraulic slave cylinder assembly inside a clutch cover, because these cylinders can leak, and the escape of the hydraulic oil can cause damage. In contrast to a pneumatically powered cylinder assembly, in which a certain amount of leakage can be readily tolerated, a hydraulic slave cylinder assembly must be leak-tight, or else the leaky hydraulic slave cylinder assembly must be repaired or replaced. Depending on the design of the hydraulic slave cylinder assembly (a ring-type hydraulic slave cylinder, for example), the corresponding repair and maintenance work may require that the drive train be separated, possibly including the removal of the clutch cover from the internal combustion engine. A disengaging system of this type appears to be too complicated for modern, electronically controlled drive trains, nor is it very satisfactory with respect to positioning accuracy.
Against this background, it is the object of the present invention to provide an actuation system of the general type described above in which the auxiliary actuating assembly is improved with respect to at least some of the aspects discussed above.
To achieve this object, in accordance with a first aspect of the invention, the auxiliary actuating assembly includes an auxiliary actuating valve assembly, which can be switched to a pressure medium feed position and/or to a pressure medium discharge position. By means of this valve assembly, the pressure medium-powered cylinder assembly can be brought into pressure medium flow connection with the pressure medium source or with a separate, auxiliary pressure medium source for the emergency actuation of the clutch (pressure medium feed position of the valve assembly) or into pressure medium flow connection with a pressure compensation port or a pressure compensation tank (pressure medium discharge position of the valve assembly).
According to the invention, the auxiliary actuation by the pressure medium-powered cylinder assembly, preferably a pneumatically powered cylinder assembly, is accomplished by means of an auxiliary actuating valve assembly, which can be switched into a pressure medium feed position, in which the pressure medium-powered cylinder assembly is in pressure medium flow connection with the pressure medium source or with a separate auxiliary pressure medium source for the emergency actuation of the clutch. Alternatively or additionally, the auxiliary actuating valve assembly can be switched to a pressure medium discharge position, in which the pressure medium-powered cylinder assembly is in pressure medium flow connection with a pressure compensation port or a pressure compensation tank for the emergency actuation of the clutch. A central auxiliary actuation function is present as soon as it becomes possible for the clutch to be disengaged by the intermediate action of the auxiliary actuating valve assembly, so that, even though a gear is engaged and the drive train is under tension, the gear can still be disengaged and the drive unit (the engine) can be started for the purpose of, for example, refilling the pneumatic or compressed air tank of the pressure medium source, which in this case is designed as a pneumatic source. Preferably, however, the clutch can be both disengaged and engaged by the intermediate action of the auxiliary actuating valve assembly. Thus it becomes possible not only for an engaged gear to be disengaged and for the drive unit to be started, but also for a gear to be made available for an emergency drive function, so that the vehicle can be driven out of a danger area or even driven to a repair garage (limp-home function). It would be ideal for the intermediate action of the auxiliary actuating valve assembly to make possible several engagements and disengagements or disengagements and engagement of the friction clutch by the appropriate switching of the auxiliary actuating valve assembly back and forth several times between the pressure medium flow position and the pressure medium discharge position. Only in this way is a truly complete limp-home function realized, in which the vehicle can move under its own power over a relatively long distance.
It is proposed that the auxiliary actuating valve assembly be switchable into the pressure medium feed position and/or into the pressure medium discharge position without the intermediate agency of the pilot/automatic control unit and/or independently of an instantaneous value of the actual value and/or independently of an instantaneous value of the control input. The auxiliary actuation of the clutch therefore does not depend on the good working order of the pilot/automatic control unit, on the good working order of a measuring device which detects the actual value, or on the good working order of a master unit which transmits the control input. So that there is no dependence on the good working order of an electronic control unit or the like, it is also preferred that the auxiliary actuating valve assembly be switchable manually by either electrical or mechanical means. It is possible, for example, to provide a simple mechanical or electrical switch, which acts directly on at least one switching valve of the auxiliary actuating valve assembly. It is also possible for the auxiliary actuating valve assembly to be switchable by the intermediate agency of the clutch pedal.
Although it is conceivable that the auxiliary actuating valve assembly could belong at least in part to the pilot/automatic control assembly, it is preferable with respect to redundancy and thus an increase in operational reliability that the auxiliary actuating valve assembly be a valve assembly separate from the pilot/automatic control valve assembly.
In a normal actuating situation, the pilot/automatic control valve assembly can be in pressure medium flow connection with the pressure medium-powered cylinder assembly by way of a switching valve assembly of the auxiliary actuating valve assembly. In an emergency actuation situation, it is preferable for the pressure medium-powered cylinder assembly to be isolated from the pilot/automatic control valve assembly by means of the switching valve assembly in order to prevent the pilot/automatic control valve assembly from interfering with the emergency actuation. If, namely, the pilot/automatic control valve assembly were to assume a pressure medium discharge position, in which, in and of itself, a pressure medium flow connection is established between the pressure medium-powered cylinder assembly and a pressure compensation port or a pressure compensation tank, and if in this situation the pilot/automatic control valve assembly could not be switched back out of this position as a result of a defect, the isolation of the pilot/automatic control valve assembly by the switching valve assembly prevents the pressure medium, which is to be supplied to the pressure medium-powered cylinder assembly for the auxiliary actuation of the clutch, from escaping via the pilot/automatic control valve assembly.
In regard to auxiliary actuation, it is proposed in particular that, in an emergency actuation situation, pressure medium can be supplied from the pressure medium source or auxiliary pressure medium source to the pressure medium-powered cylinder assembly or that pressure medium can be discharged from the pressure medium-powered cylinder via a/the switching valve assembly. For this purpose, it is proposed as an especially preferred elaboration that, in a first switching position of the switching valve assembly, pressure medium can be supplied from the pressure medium source to the pressure medium-powered cylinder assembly and that, in a second switching position of the switching valve assembly, pressure medium can be supplied from the auxiliary pressure medium source to the pressure medium-powered cylinder assembly. According to this proposal, therefore, an auxiliary pressure medium source is provided in addition to the pressure medium source; this auxiliary source then supplies for example, the pressure medium-powered cylinder assembly when the pressure medium source can no longer provide pressure medium at sufficient pressure. For this purpose, it is especially advisable for the auxiliary pressure medium source to comprise an auxiliary pressure medium tank.
It is preferable that it be possible for the auxiliary pressure medium tank to be filled by the pressure medium source. For this purpose it is specifically proposed that, in a normal operating state or a regeneration operating state of the actuation system, pressure medium can be supplied from the pressure medium source to the auxiliary pressure medium tank via a/the switching valve assembly of the auxiliary actuating valve assembly and can be stored in the auxiliary pressure medium tank. To counteract the gradual emptying of the auxiliary pressure medium tank as a result of leakage in the pressure medium system, it is especially advisable to provide the auxiliary pressure medium tank with a switching or shutoff valve assembly, by means of which the tank can be isolated from the rest of the pressure medium system.
A control/diagnosis unit can be provided, which serves to detect and evaluate the pressure of the pressure medium provided by the pressure source and/or the pressure of the pressure medium in at least one pressure medium receiver circuit and/or the pressure of the pressure medium of the auxiliary pressure medium tank and/or to monitor the working order of the pilot/automatic control valve assembly and/or the working order of the pilot/automatic control unit which controls the pilot/automatic control valve assembly. This control/diagnosis unit then serves, as a function of these data, to operate a vehicle information system and/or at least one valve of the actuation system and/or to block or to enable a normal clutch actuation and/or to block or to enable an emergency clutch actuation and/or to initiate the filling of the auxiliary pressure medium tank.
The control/diagnosis unit preferably monitors a position control circuit of the pressure medium-powered cylinder assembly, this circuit comprising the pilot/automatic control valve assembly and, if desired, the pilot/automatic control unit, to determine whether or not an actual position value has been adjusted to a predetermined desired position value in agreement with a predetermined agreement criterion within a predetermined desired actuating time. This control/diagnosis unit then serves to operate, as a function of these data, a vehicle information system and/or at least one valve of the actuation system and/or to block or to enable a normal clutch actuation and/or to block or to enable an emergency clutch actuation. This proposal is based on the insight that there is no need for a detailed error analysis as a basis for switching from a normal clutch actuation mode in an emergency to an auxiliary clutch actuation mode. Whatever the defect, it will always reveal itself at least by the fact that the automatic position control circuit has failed to adjust the actual position value back to the desired position value sufficiently within a desired adjusting time. The agreement criterion can specify that the actual position value should be essentially the same as the desired position value, possibly within a certain allowable tolerance range. In the case of a system which is designed to eliminate the difference between the actual position value and desired position value within approximately 150 ms, for example, it is possible to specify a value of 200 ms for the desired adjusting time.
The blocking of normal clutch actuation can comprise a compulsory switching of a shutoff valve assembly into a blocking condition, in which a first pressure medium subsystem comprising the pilot/automatic control valve assembly is isolated from a second pressure medium subsystem comprising the pressure medium-powered cylinder assembly and the auxiliary actuating valve assembly. The enabling of normal clutch actuation can comprise a switching of a/the shutoff valve assembly to a connecting condition, in which a/the first pressure medium subsystem comprising the pilot/automatic control valve assembly is connected to a/the second pressure medium subsystem comprising the pressure medium-powered cylinder assembly and the auxiliary actuating valve assembly via the shutoff valve assembly.
The enabling of auxiliary clutch actuation can release the auxiliary actuating valve assembly so that it can switch as desired either to the pressure medium feed position or to the pressure medium discharge position. The blocking of auxiliary clutch actuation can comprise a compulsory switching of the auxiliary actuating valve assembly to a neutral position (possibly corresponding to a hold position in auxiliary actuation mode), in which the auxiliary actuating valve assembly allows no pressure medium feed to the pressure medium-powered cylinder assembly and no pressure medium discharge from the pressure medium-powered cylinder assembly.
According to a preferred embodiment, the auxiliary actuating valve assembly and/or the shutoff valve assembly is designed and connected so that normal clutch actuation is blocked and the auxiliary clutch actuation is enabled when at least one predetermined error criterion is fulfilled. What is intended here in particular is that the error criterion pertain to the existence of at least one signal which is transmitted by the control/diagnosis unit and which possibly encodes the normal clutch actuation mode and/or the auxiliary clutch actuation mode. In addition, it will usually be advisable for an error criterion to pertain to the availability of the minimum pressure medium pressure required for normal actuation of the clutch.
It is also proposed that an error criterion pertain to the good working order of the electronic pilot/automatic control circuitry and of the pilot/automatic control valve assembly. The error criterion can also pertain to the adjusting of the actual position value to the predetermined desired position value in agreement with the predetermined agreement criterion within the predetermined desired adjusting time.
In accordance with a second aspect of the invention, it is proposed in conjunction with the previously described actuation system, which is not necessarily equipped with an auxiliary actuating assembly, to provide a shutoff or switching valve assembly associated with the pressure medium tank of the pressure medium source and/or a separate auxiliary pressure medium tank of the auxiliary actuating assembly be provided. By means of this valve assembly a pressure medium subsystem comprising at least one pressure medium receiver can be connected to the tank, and the tank can be isolated at least during relatively long idle periods of the vehicle from the pressure medium subsystem in order to prevent the tank from slowly emptying as a result of leakage in the pressure medium subsystem. When this proposal is implemented, leakage in the pressure medium subsystem, specifically leakage in one or more pressure medium users, no longer plays a role with respect to the service life of the tank. The service life of the tank now depends only on the leak-tightness of the tank itself, on the leak-tightness of any pressure medium connection between the shutoff or switching valve assembly and the tank, and on the leak-tightness of the shutoff or switching valve assembly. Even though, as mentioned, this idea of the invention can be applied to the pressure medium tank of the pressure medium source, the primary intention is that it be applied to the auxiliary tank of the auxiliary actuating assembly separate from the pressure medium source. The shutoff or switching valve assembly will then be assigned to this auxiliary pressure medium tank.
In accordance with a third aspect of the invention, the auxiliary actuating assembly includes an auxiliary pressure medium tank separate from the pressure source, which tank can be brought into pressure medium flow connection with the pressure medium source via an associated valve assembly in order to fill the auxiliary pressure medium tank with pressure medium. This auxiliary tank can be brought via the valve into pressure medium flow connection with the pressure medium-powered cylinder assembly in order to actuate the clutch, preferably to disconnect it. The auxiliary tank can be isolated by means of the valve assembly from the rest of the pressure medium system, including the pressure medium source and the pressure medium-powered cylinder assembly, in order to keep the pressure medium in the auxiliary pressure medium tank available for use in emergency actuation situations. The auxiliary pressure medium tank makes it possible for the clutch to be actuated in auxiliary mode independently of the pressure medium source.
The valve assembly preferably has at least one nonreturn valve, which, as a function of at least one pressure medium pressure being applied to it, enables and blocks the pressure medium flow connection between the pressure medium source and the auxiliary pressure medium tank. It is advantageous for the assembly to be designed so that a valve does not have to be actuated separately to fill the auxiliary pressure medium tank, but rather so that the nonreturn valve always opens automatically to allow the filling of the auxiliary pressure medium tank whenever the pressure medium source is supplying sufficient pressure.
The pressure medium-powered cylinder assembly can preferably be brought into pressure medium flow connection with a pressure compensation port or a pressure compensation tank via a/the associated valve assembly in order to actuate the clutch, preferably to engage it.
It is advantageous to provide a throttle point in a pressure medium flow connection associated with the pressure medium-powered cylinder assembly, so that an auxiliary clutch-engaging time and/or an auxiliary clutch-disengaging time can be set.
In regard to the auxiliary pressure medium tank, it is proposed that it be designed to store a volume of pressure medium which is sufficient for at least two, preferably for at least three to five clutch actuations, each actuation including one disengagement of the pressure medium-powered cylinder assembly. In the case that the auxiliary tank holds compressed air, a suitable volume would be, for example, approximately 2 liters or so.
The invention under the first, second, and third aspects can be used independently of the type and design of the pilot/automatic control valve assembly, of the type and design of the conventional measuring system for detecting the actual actuation state, and of the type and design of any pilot/automatic control unit which may be provided. Thus, the invention can be used in an actuation system with a hydraulic measuring cylinder assembly and with a pilot/automatic control valve assembly working according to the principle of the pressure scale as described in DE 197 16 600 in order to make emergency actuation of the clutch possible without the need to design the hydraulic measuring cylinder assembly as a hydraulic slave cylinder assembly or without the need to provide a separate hydraulic slave cylinder assembly. The invention will, however, be especially advantageous when it is associated with electrical pilot/automatic control valve assemblies or magnetic pilot/automatic control valve assemblies comprising at least one proportional pilot/automatic control valve or at least one electrically actuated switching valve (such as that described in U.S. Pat. No. 5,004,086). Various designs and functional principles which can be considered for the actuation system and various possibilities for representing the actual value and the control input are described in DE 197 16 600.
The invention also pertains to a drive train for a motor vehicle, especially a commercial motor vehicle, comprising a drive unit, a transmission, a friction clutch installed between the drive unit and the transmission, and an actuation system of the type described above.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.